Devices, Systems, and Methods for Assessing a Vessel

ABSTRACT

Embodiments of the present disclosure are configured to assess the severity of a blockage in a vessel and, in particular, a stenosis in a blood vessel. In some particular embodiments, the devices, systems, and methods of the present disclosure are configured to assess the severity of a stenosis in the coronary arteries without the administration of a hyperemic agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/460,296, filed Apr. 30, 2012, which claims priority to andthe benefit of U.S. Provisional Patent Application No. 61/525,736 filedon Aug. 20, 2011 and U.S. Provisional Patent Application No. 61/525,739filed on Aug. 20, 2011, each of which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the assessment of vesselsand, in particular, the assessment of the severity of a blockage orother restriction to the flow of fluid through a vessel. Aspects of thepresent disclosure are particularly suited for evaluation of biologicalvessels in some instances. For example, some particular embodiments ofthe present disclosure are specifically configured for the evaluation ofa stenosis of a human blood vessel.

BACKGROUND

A currently accepted technique for assessing the severity of a stenosisin a blood vessel, including ischemia causing lesions, is fractionalflow reserve (FFR). FFR is a calculation of the ratio of a distalpressure measurement (taken on the distal side of the stenosis) relativeto a proximal pressure measurement (taken on the proximal side of thestenosis). FFR provides an index of stenosis severity that allowsdetermination as to whether the blockage limits blood flow within thevessel to an extent that treatment is required. The normal value of FFRin a healthy vessel is 1.00, while values less than about 0.80 aregenerally deemed significant and require treatment. Common treatmentoptions include angioplasty and stenting.

Coronary blood flow is unique in that it is affected not only byfluctuations in the pressure arising proximally (as in the aorta) but isalso simultaneously affected by fluctuations arising distally in themicrocirculation. Accordingly, it is not possible to accurately assessthe severity of a coronary stenosis by simply measuring the fall in meanor peak pressure across the stenosis because the distal coronarypressure is not purely a residual of the pressure transmitted from theaortic end of the vessel. As a result, for an effective calculation ofFFR within the coronary arteries, it is necessary to reduce the vascularresistance within the vessel. Currently, pharmacological hyperemicagents, such as adenosine, are administered to reduce and stabilize theresistance within the coronary arteries. These potent vasodilator agentsreduce the dramatic fluctuation in resistance (predominantly by reducingthe microcirculation resistance associated with the systolic portion ofthe heart cycle) to obtain a relatively stable and minimal resistancevalue.

However, the administration of hyperemic agents is not always possibleor advisable. First, the clinical effort of administering hyperemicagents can be significant. In some countries (particularly the UnitedStates), hyperemic agents such as adenosine are expensive, and timeconsuming to obtain when delivered intravenously (IV). In that regard,IV-delivered adenosine is generally mixed on a case-by-case basis in thehospital pharmacy. It can take a significant amount of time and effortto get the adenosine prepared and delivered to the operating area. Theselogistic hurdles can impact a physician's decision to use FFR. Second,some patients have contraindications to the use of hyperemic agents suchas asthma, severe COPD, hypotension, bradycardia, low cardiac ejectionfraction, recent myocardial infarction, and/or other factors thatprevent the administration of hyperemic agents. Third, many patientsfind the administration of hyperemic agents to be uncomfortable, whichis only compounded by the fact that the hyperemic agent may need to beapplied multiple times during the course of a procedure to obtain FFRmeasurements. Fourth, the administration of a hyperemic agent may alsorequire central venous access (e.g., a central venous sheath) that mightotherwise be avoided. Finally, not all patients respond as expected tohyperemic agents and, in some instances, it is difficult to identifythese patients before administration of the hyperemic agent.

Accordingly, there remains a need for improved devices, systems, andmethods for assessing the severity of a blockage in a vessel and, inparticular, a stenosis in a blood vessel. In that regard, there remainsa need for improved devices, systems, and methods for assessing theseverity of a stenosis in the coronary arteries that do not require theadministration of hyperemic agents.

SUMMARY

Embodiments of the present disclosure are configured to assess theseverity of a blockage in a vessel and, in particular, a stenosis in ablood vessel. In some particular embodiments, the devices, systems, andmethods of the present disclosure are configured to assess the severityof a stenosis in the coronary arteries without the administration of ahyperemic agent.

In some instances, a method of evaluating a vessel of a patient isprovided. The method includes introducing at least one instrument intothe vessel of the patient; obtaining from the at least one instrumentproximal pressure measurements within the vessel at a position proximalof a stenosis of the vessel for at least one cardiac cycle of thepatient; obtaining from the at least one instrument distal pressuremeasurements within the vessel at a position distal of the stenosis ofthe vessel for the at least one cardiac cycle of the patient; selectinga diagnostic window within a cardiac cycle of the patient, wherein thediagnostic window encompassing only a portion of the cardiac cycle ofthe patient; and calculating a pressure ratio between the distalpressure measurements obtained during the diagnostic window and theproximal pressure measurements obtained during the diagnostic window. Insome embodiments, the diagnostic window is selected at least partiallybased on one or more characteristics of the proximal pressuremeasurements. For example, a starting point and/or an ending point ofthe diagnostic window is selected based on the proximal pressuremeasurements. In that regard, the starting and/or ending point is basedon one or more of a dicrotic notch in the proximal pressuremeasurements, a peak pressure of the proximal pressure measurements, amaximum change in pressure of the proximal pressure measurements, astart of a cardiac cycle of the proximal pressure measurements, and astart of diastole of the proximal pressure measurements. In someinstances, an ending point of the diagnostic window is selected to be afixed amount of time from the starting point.

In some embodiments, the diagnostic window is selected at leastpartially based on one or more characteristics of the distal pressuremeasurements. For example, a starting point and/or an ending point ofthe diagnostic window is selected based on the distal pressuremeasurements. In that regard, the starting and/or ending point is basedon one or more of a dicrotic notch in the distal pressure measurements,a peak pressure of the distal pressure measurements, a maximum change inpressure of the distal pressure measurements, a start of a cardiac cycleof the distal pressure measurements, a ventricularization point of thedistal pressure measurements, and a start of diastole of the distalpressure measurements. In some instances, the diagnostic window isselected by identifying a maximum diagnostic window and selecting aportion of the maximum diagnostic window as the diagnostic window.Further, in some embodiments, the method further comprises obtainingfrom the at least one instrument flow velocity measurements of a fluidflowing through the vessel. In that regard, the diagnostic window isselected, in some instances, to correspond to a portion of the cardiaccycle where a differential, first derivative, and/or second derivativeof the flow velocity measurements has a relatively constant value ofapproximately zero. In some embodiments, the diagnostic window isselected based on characteristics of an ECG signal of the patient. Insome embodiments, the heart of the patient is not stressed during the atleast one cardiac cycle in which the proximal and distal pressuremeasurements are taken. Further, in some embodiments, the method furthercomprises temporally aligning at least a portion of the proximalpressure measurements with at least a portion of the distal pressuremeasurements.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure will be describedwith reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic perspective view of a vessel having a stenosisaccording to an embodiment of the present disclosure.

FIG. 2 is a diagrammatic, partial cross-sectional perspective view of aportion of the vessel of FIG. 1 taken along section line 2-2 of FIG. 1.

FIG. 3 is a diagrammatic, partial cross-sectional perspective view ofthe vessel of FIGS. 1 and 2 with instruments positioned thereinaccording to an embodiment of the present disclosure.

FIG. 4 is a diagrammatic, schematic view of a system according to anembodiment of the present disclosure.

FIG. 5 is a graphical representation of measured pressure, velocity, andresistance within a vessel according to an embodiment of the presentdisclosure.

FIG. 6 is a magnified view of a portion of the graphical representationof FIG. 5 corresponding to a resting state of a patient.

FIG. 7 is a magnified view of a portion of the graphical representationof FIG. 5 corresponding to a hyperemic state of a patient.

FIG. 8 is the portion of the graphical representation of FIG. 6annotated to identify a diagnostic window according to an embodiment ofthe present disclosure.

FIG. 9 is a graphical representation of measured pressure and velocitywithin a vessel according to an embodiment of the present disclosure.

FIG. 10 is a graphical representation of a derivative of the measuredvelocity of FIG. 9 according to an embodiment of the present disclosure.

FIG. 11 is the graphical representation of FIG. 9 annotated to identifya diagnostic window according to an embodiment of the presentdisclosure.

FIG. 12 is a graphical representation of wave intensity within a vesselaccording to an embodiment of the present disclosure.

FIG. 13 is a graphical representation of proximal and distal originatingpressure waves within a vessel corresponding to the wave intensity ofFIG. 12 according to an embodiment of the present disclosure.

FIG. 14 is a graphical representation of pressure and velocity within avessel corresponding to the wave intensity of FIG. 12 and the proximaland distal originating pressure waves of FIG. 13 according to anembodiment of the present disclosure.

FIG. 15 is a graphical representation of a resistance within a vesselcorresponding to the wave intensity of FIG. 12, the proximal and distaloriginating pressure waves of FIG. 13, and the pressure and velocity ofFIG. 14 according to an embodiment of the present disclosure.

FIG. 16 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a proximal pressure measurementaccording to an embodiment of the present disclosure.

FIG. 17 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a proximal pressure measurementaccording to another embodiment of the present disclosure.

FIG. 18 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a proximal pressure measurementaccording to another embodiment of the present disclosure.

FIG. 19 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a distal pressure measurementaccording to an embodiment of the present disclosure.

FIG. 20 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a distal pressure measurementaccording to another embodiment of the present disclosure.

FIG. 21 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a distal pressure measurementaccording to another embodiment of the present disclosure.

FIG. 22 is a graphical representation of an identification of a startingpoint of a diagnostic window based on a distal pressure measurementaccording to another embodiment of the present disclosure.

FIG. 23 is a graphical representation of an identification of an endingpoint of a diagnostic window based on a starting point of the diagnosticwindow according to an embodiment of the present disclosure.

FIG. 24 is a graphical representation of an identification of an endingpoint of a diagnostic window based on a proximal pressure measurementaccording to an embodiment of the present disclosure.

FIG. 25 is a graphical representation of an identification of an endingpoint of a diagnostic window based on a distal pressure measurementaccording to an embodiment of the present disclosure.

FIG. 26 is a graphical representation of an identification of an endingpoint of a diagnostic window based on a distal pressure measurementaccording to an embodiment of the present disclosure.

FIG. 27 is a graphical representation of a diagnostic window relative toproximal and distal pressure measurements according to an embodiment ofthe present disclosure.

FIG. 28 is a graphical representation of a diagnostic window relative toproximal and distal pressure measurements according to anotherembodiment of the present disclosure.

FIG. 29 is graphical representation of an ECG signal according to anembodiment of the present disclosure.

FIG. 30 is a graphical representation of a diagnostic window relative toproximal and distal pressure measurements according to anotherembodiment of the present disclosure.

FIG. 31 is a graphical representation of a diagnostic window relative toproximal and distal pressure measurements according to an embodiment ofthe present disclosure.

FIG. 32 is a magnified view of a portion of the graphical representationof FIG. 30 illustrating a temporal adjustment of the distal pressuremeasurement relative to the proximal pressure measurement.

FIG. 33 is a graphical representation of proximal and distal pressuremeasurements within a vessel according to an embodiment of the presentdisclosure.

FIG. 34 is a pair of graphical representations, where the top graphicalrepresentation illustrates proximal and distal pressure measurementswithin a vessel and the bottom graphical representation illustrates aratio of the proximal and distal pressure measurements and a fit betweenthe proximal pressure waveform and the distal pressure waveformaccording to an embodiment of the present disclosure.

FIG. 35 is a pair of graphical representations similar to that of FIG.33, but where the distal pressure measurement waveform of the topgraphical representation has been shifted relative the distal pressurewaveform of FIG. 33 and the bottom graphical representation illustratesthe corresponding ratio of the proximal and distal pressure measurementsand the fit between the proximal pressure waveform and the distalpressure waveform based on the shifted distal pressure measurementwaveform.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. In particular, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure. For the sake ofbrevity, however, the numerous iterations of these combinations will notbe described separately.

Referring to FIGS. 1 and 2, shown therein is a vessel 100 having astenosis according to an embodiment of the present disclosure. In thatregard, FIG. 1 is a diagrammatic perspective view of the vessel 100,while FIG. 2 is a partial cross-sectional perspective view of a portionof the vessel 100 taken along section line 2-2 of FIG. 1. Referring morespecifically to FIG. 1, the vessel 100 includes a proximal portion 102and a distal portion 104. A lumen 106 extends along the length of thevessel 100 between the proximal portion 102 and the distal portion 104.In that regard, the lumen 106 is configured to allow the flow of fluidthrough the vessel. In some instances, the vessel 100 is a systemicblood vessel. In some particular instances, the vessel 100 is a coronaryartery. In such instances, the lumen 106 is configured to facilitate theflow of blood through the vessel 100.

As shown, the vessel 100 includes a stenosis 108 between the proximalportion 102 and the distal portion 104. Stenosis 108 is generallyrepresentative of any blockage or other structural arrangement thatresults in a restriction to the flow of fluid through the lumen 106 ofthe vessel 100. Embodiments of the present disclosure are suitable foruse in a wide variety of vascular applications, including withoutlimitation coronary, peripheral (including but not limited to lowerlimb, carotid, and neurovascular), renal, and/or venous. Where thevessel 100 is a blood vessel, the stenosis 108 may be a result of plaquebuildup, including without limitation plaque components such as fibrous,fibro-lipidic (fibro fatty), necrotic core, calcified (dense calcium),blood, fresh thrombus, and mature thrombus. Generally, the compositionof the stenosis will depend on the type of vessel being evaluated. Inthat regard, it is understood that the concepts of the presentdisclosure are applicable to virtually any type of blockage or othernarrowing of a vessel that results in decreased fluid flow.

Referring more particularly to FIG. 2, the lumen 106 of the vessel 100has a diameter 110 proximal of the stenosis 108 and a diameter 112distal of the stenosis. In some instances, the diameters 110 and 112 aresubstantially equal to one another. In that regard, the diameters 110and 112 are intended to represent healthy portions, or at leasthealthier portions, of the lumen 106 in comparison to stenosis 108.Accordingly, these healthier portions of the lumen 106 are illustratedas having a substantially constant cylindrical profile and, as a result,the height or width of the lumen has been referred to as a diameter.However, it is understood that in many instances these portions of thelumen 106 will also have plaque buildup, a non-symmetric profile, and/orother irregularities, but to a lesser extent than stenosis 108 and,therefore, will not have a cylindrical profile. In such instances, thediameters 110 and 112 are understood to be representative of a relativesize or cross-sectional area of the lumen and do not imply a circularcross-sectional profile.

As shown in FIG. 2, stenosis 108 includes plaque buildup 114 thatnarrows the lumen 106 of the vessel 100. In some instances, the plaquebuildup 114 does not have a uniform or symmetrical profile, makingangiographic evaluation of such a stenosis unreliable. In theillustrated embodiment, the plaque buildup 114 includes an upper portion116 and an opposing lower portion 118. In that regard, the lower portion118 has an increased thickness relative to the upper portion 116 thatresults in a non-symmetrical and non-uniform profile relative to theportions of the lumen proximal and distal of the stenosis 108. As shown,the plaque buildup 114 decreases the available space for fluid to flowthrough the lumen 106. In particular, the cross-sectional area of thelumen 106 is decreased by the plaque buildup 114. At the narrowest pointbetween the upper and lower portions 116, 118 the lumen 106 has a height120, which is representative of a reduced size or cross-sectional arearelative to the diameters 110 and 112 proximal and distal of thestenosis 108. Note that the stenosis 108, including plaque buildup 114is exemplary in nature and should be considered limiting in any way. Inthat regard, it is understood that the stenosis 108 has other shapesand/or compositions that limit the flow of fluid through the lumen 106in other instances. While the vessel 100 is illustrated in FIGS. 1 and 2as having a single stenosis 108 and the description of the embodimentsbelow is primarily made in the context of a single stenosis, it isnevertheless understood that the devices, systems, and methods describedherein have similar application for a vessel having multiple stenosisregions.

Referring now to FIG. 3, the vessel 100 is shown with instruments 130and 132 positioned therein according to an embodiment of the presentdisclosure. In general, instruments 130 and 132 may be any form ofdevice, instrument, or probe sized and shaped to be positioned within avessel. In the illustrated embodiment, instrument 130 is generallyrepresentative of a guide wire, while instrument 132 is generallyrepresentative of a catheter. In that regard, instrument 130 extendsthrough a central lumen of instrument 132. However, in otherembodiments, the instruments 130 and 132 take other forms. In thatregard, the instruments 130 and 132 are of similar form in someembodiments. For example, in some instances, both instruments 130 and132 are guide wires. In other instances, both instruments 130 and 132are catheters. On the other hand, the instruments 130 and 132 are ofdifferent form in some embodiments, such as the illustrated embodiment,where one of the instruments is a catheter and the other is a guidewire. Further, in some instances, the instruments 130 and 132 aredisposed coaxial with one another, as shown in the illustratedembodiment of FIG. 3. In other instances, one of the instruments extendsthrough an off-center lumen of the other instrument. In yet otherinstances, the instruments 130 and 132 extend side-by-side. In someparticular embodiments, at least one of the instruments is as arapid-exchange device, such as a rapid-exchange catheter. In suchembodiments, the other instrument is a buddy wire or other deviceconfigured to facilitate the introduction and removal of therapid-exchange device. Further still, in other instances, instead of twoseparate instruments 130 and 132 a single instrument is utilized. Inthat regard, the single instrument incorporates aspects of thefunctionalities (e.g., data acquisition) of both instruments 130 and 132in some embodiments.

Instrument 130 is configured to obtain diagnostic information about thevessel 100. In that regard, the instrument 130 includes one or moresensors, transducers, and/or other monitoring elements configured toobtain the diagnostic information about the vessel. The diagnosticinformation includes one or more of pressure, flow (velocity), images(including images obtained using ultrasound (e.g., IVUS), OCT, thermal,and/or other imaging techniques), temperature, and/or combinationsthereof. The one or more sensors, transducers, and/or other monitoringelements are positioned adjacent a distal portion of the instrument 130in some instances. In that regard, the one or more sensors, transducers,and/or other monitoring elements are positioned less than 30 cm, lessthan 10 cm, less than 5 cm, less than 3 cm, less than 2 cm, and/or lessthan 1 cm from a distal tip 134 of the instrument 130 in some instances.In some instances, at least one of the one or more sensors, transducers,and/or other monitoring elements is positioned at the distal tip of theinstrument 130.

The instrument 130 includes at least one element configured to monitorpressure within the vessel 100. The pressure monitoring element can takethe form a piezo-resistive pressure sensor, a piezo-electric pressuresensor, a capacitive pressure sensor, an electromagnetic pressuresensor, a fluid column (the fluid column being in communication with afluid column sensor that is separate from the instrument and/orpositioned at a portion of the instrument proximal of the fluid column),an optical pressure sensor, and/or combinations thereof. In someinstances, one or more features of the pressure monitoring element areimplemented as a solid-state component manufactured using semiconductorand/or other suitable manufacturing techniques. Examples of commerciallyavailable guide wire products that include suitable pressure monitoringelements include, without limitation, the PrimeWire PRESTIGE® pressureguide wire, the PrimeWire® pressure guide wire, and the ComboWire® XTpressure and flow guide wire, each available from Volcano Corporation,as well as the PressureWire™ Certus guide wire and the PressureWire™Aeris guide wire, each available from St. Jude Medical, Inc. Generally,the instrument 130 is sized such that it can be positioned through thestenosis 108 without significantly impacting fluid flow across thestenosis, which would impact the distal pressure reading. Accordingly,in some instances the instrument 130 has an outer diameter of 0.018″ orless. In some embodiments, the instrument 130 has an outer diameter of0.014″ or less.

Instrument 132 is also configured to obtain diagnostic information aboutthe vessel 100. In some instances, instrument 132 is configured toobtain the same diagnostic information as instrument 130. In otherinstances, instrument 132 is configured to obtain different diagnosticinformation than instrument 130, which may include additional diagnosticinformation, less diagnostic information, and/or alternative diagnosticinformation. The diagnostic information obtained by instrument 132includes one or more of pressure, flow (velocity), images (includingimages obtained using ultrasound (e.g., IVUS), OCT, thermal, and/orother imaging techniques), temperature, and/or combinations thereof.Instrument 132 includes one or more sensors, transducers, and/or othermonitoring elements configured to obtain this diagnostic information. Inthat regard, the one or more sensors, transducers, and/or othermonitoring elements are positioned adjacent a distal portion of theinstrument 132 in some instances. In that regard, the one or moresensors, transducers, and/or other monitoring elements are positionedless than 30 cm, less than 10 cm, less than 5 cm, less than 3 cm, lessthan 2 cm, and/or less than 1 cm from a distal tip 136 of the instrument132 in some instances. In some instances, at least one of the one ormore sensors, transducers, and/or other monitoring elements ispositioned at the distal tip of the instrument 132.

Similar to instrument 130, instrument 132 also includes at least oneelement configured to monitor pressure within the vessel 100. Thepressure monitoring element can take the form a piezo-resistive pressuresensor, a piezo-electric pressure sensor, a capacitive pressure sensor,an electromagnetic pressure sensor, a fluid column (the fluid columnbeing in communication with a fluid column sensor that is separate fromthe instrument and/or positioned at a portion of the instrument proximalof the fluid column), an optical pressure sensor, and/or combinationsthereof. In some instances, one or more features of the pressuremonitoring element are implemented as a solid-state componentmanufactured using semiconductor and/or other suitable manufacturingtechniques. Millar catheters are utilized in some embodiments. Currentlyavailable catheter products suitable for use with one or more ofPhilips's Xper Flex Cardio Physiomonitoring System, GE's Mac-Lab XT andXTi hemodynamic recording systems, Siemens's AXIOM Sensis XP VC11,McKesson's Horizon Cardiology Hemo, and Mennen's Horizon XVu HemodynamicMonitoring System and include pressure monitoring elements can beutilized for instrument 132 in some instances.

In accordance with aspects of the present disclosure, at least one ofthe instruments 130 and 132 is configured to monitor a pressure withinthe vessel 100 distal of the stenosis 108 and at least one of theinstruments 130 and 132 is configured to monitor a pressure within thevessel proximal of the stenosis. In that regard, the instruments 130,132 are sized and shaped to allow positioning of the at least oneelement configured to monitor pressure within the vessel 100 to bepositioned proximal and/or distal of the stenosis 108 as necessary basedon the configuration of the devices. In that regard, FIG. 3 illustratesa position 138 suitable for measuring pressure distal of the stenosis108. In that regard, the position 138 is less than 5 cm, less than 3 cm,less than 2 cm, less than 1 cm, less than 5 mm, and/or less than 2.5 mmfrom the distal end of the stenosis 108 (as shown in FIG. 2) in someinstances. FIG. 3 also illustrates a plurality of suitable positions formeasuring pressure proximal of the stenosis 108. In that regard,positions 140, 142, 144, 146, and 148 each represent a position that issuitable for monitoring the pressure proximal of the stenosis in someinstances. In that regard, the positions 140, 142, 144, 146, and 148 arepositioned at varying distances from the proximal end of the stenosis108 ranging from more than 20 cm down to about 5 mm or less. Generally,the proximal pressure measurement will be spaced from the proximal endof the stenosis. Accordingly, in some instances, the proximal pressuremeasurement is taken at a distance equal to or greater than an innerdiameter of the lumen of the vessel from the proximal end of thestenosis. In the context of coronary artery pressure measurements, theproximal pressure measurement is generally taken at a position proximalof the stenosis and distal of the aorta, within a proximal portion ofthe vessel. However, in some particular instances of coronary arterypressure measurements, the proximal pressure measurement is taken from alocation inside the aorta. In other instances, the proximal pressuremeasurement is taken at the root or ostium of the coronary artery.

Referring now to FIG. 4, shown therein is a system 150 according to anembodiment of the present disclosure. In that regard, FIG. 4 is adiagrammatic, schematic view of the system 150. As shown, the system 150includes an instrument 152. In that regard, in some instances instrument152 is suitable for use as at least one of instruments 130 and 132discussed above. Accordingly, in some instances the instrument 152includes features similar to those discussed above with respect toinstruments 130 and 132 in some instances. In the illustratedembodiment, the instrument 152 is a guide wire having a distal portion154 and a housing 156 positioned adjacent the distal portion. In thatregard, the housing 156 is spaced approximately 3 cm from a distal tipof the instrument 152. The housing 156 is configured to house one ormore sensors, transducers, and/or other monitoring elements configuredto obtain the diagnostic information about the vessel. In theillustrated embodiment, the housing 156 contains at least a pressuresensor configured to monitor a pressure within a lumen in which theinstrument 152 is positioned. A shaft 158 extends proximally from thehousing 156. A torque device 160 is positioned over and coupled to aproximal portion of the shaft 158. A proximal end portion 162 of theinstrument 152 is coupled to a connector 164. A cable 166 extends fromconnector 164 to a connector 168. In some instances, connector 168 isconfigured to be plugged into an interface 170. In that regard,interface 170 is a patient interface module (PIM) in some instances. Insome instances, the cable 166 is replaced with a wireless connection. Inthat regard, it is understood that various communication pathwaysbetween the instrument 152 and the interface 170 may be utilized,including physical connections (including electrical, optical, and/orfluid connections), wireless connections, and/or combinations thereof.

The interface 170 is communicatively coupled to a computing device 172via a connection 174. Computing device 172 is generally representativeof any device suitable for performing the processing and analysistechniques discussed within the present disclosure. In some embodiments,the computing device 172 includes a processor, random access memory, anda storage medium. In that regard, in some particular instances thecomputing device 172 is programmed to execute steps associated with thedata acquisition and analysis described herein. Accordingly, it isunderstood that any steps related to data acquisition, data processing,instrument control, and/or other processing or control aspects of thepresent disclosure may be implemented by the computing device usingcorresponding instructions stored on or in a non-transitory computerreadable medium accessible by the computing device. In some instances,the computing device 172 is a console device. In some particularinstances, the computing device 172 is similar to the s5™ Imaging Systemor the s5i™ Imaging System, each available from Volcano Corporation. Insome instances, the computing device 172 is portable (e.g., handheld, ona rolling cart, etc.). Further, it is understood that in some instancesthe computing device 172 comprises a plurality of computing devices. Inthat regard, it is particularly understood that the different processingand/or control aspects of the present disclosure may be implementedseparately or within predefined groupings using a plurality of computingdevices. Any divisions and/or combinations of the processing and/orcontrol aspects described below across multiple computing devices arewithin the scope of the present disclosure.

Together, connector 164, cable 166, connector 168, interface 170, andconnection 174 facilitate communication between the one or more sensors,transducers, and/or other monitoring elements of the instrument 152 andthe computing device 172. However, this communication pathway isexemplary in nature and should not be considered limiting in any way. Inthat regard, it is understood that any communication pathway between theinstrument 152 and the computing device 172 may be utilized, includingphysical connections (including electrical, optical, and/or fluidconnections), wireless connections, and/or combinations thereof. In thatregard, it is understood that the connection 174 is wireless in someinstances. In some instances, the connection 174 includes acommunication link over a network (e.g., intranet, internet,telecommunications network, and/or other network). In that regard, it isunderstood that the computing device 172 is positioned remote from anoperating area where the instrument 152 is being used in some instances.Having the connection 174 include a connection over a network canfacilitate communication between the instrument 152 and the remotecomputing device 172 regardless of whether the computing device is in anadjacent room, an adjacent building, or in a different state/country.Further, it is understood that the communication pathway between theinstrument 152 and the computing device 172 is a secure connection insome instances. Further still, it is understood that, in some instances,the data communicated over one or more portions of the communicationpathway between the instrument 152 and the computing device 172 isencrypted.

The system 150 also includes an instrument 175. In that regard, in someinstances instrument 175 is suitable for use as at least one ofinstruments 130 and 132 discussed above. Accordingly, in some instancesthe instrument 175 includes features similar to those discussed abovewith respect to instruments 130 and 132 in some instances. In theillustrated embodiment, the instrument 175 is a catheter-type device. Inthat regard, the instrument 175 includes one or more sensors,transducers, and/or other monitoring elements adjacent a distal portionof the instrument configured to obtain the diagnostic information aboutthe vessel. In the illustrated embodiment, the instrument 175 includes apressure sensor configured to monitor a pressure within a lumen in whichthe instrument 175 is positioned. The instrument 175 is in communicationwith an interface 176 via connection 177. In some instances, interface176 is a hemodynamic monitoring system or other control device, such asSiemens AXIOM Sensis, Mennen Horizon XVu, and Philips Xper IMPhysiomonitoring 5. In one particular embodiment, instrument 175 is apressure-sensing catheter that includes fluid column extending along itslength. In such an embodiment, interface 176 includes a hemostasis valvefluidly coupled to the fluid column of the catheter, a manifold fluidlycoupled to the hemostasis valve, and tubing extending between thecomponents as necessary to fluidly couple the components. In thatregard, the fluid column of the catheter is in fluid communication witha pressure sensor via the valve, manifold, and tubing. In someinstances, the pressure sensor is part of interface 176. In otherinstances, the pressure sensor is a separate component positionedbetween the instrument 175 and the interface 176. The interface 176 iscommunicatively coupled to the computing device 172 via a connection178.

Similar to the connections between instrument 152 and the computingdevice 172, interface 176 and connections 177 and 178 facilitatecommunication between the one or more sensors, transducers, and/or othermonitoring elements of the instrument 175 and the computing device 172.However, this communication pathway is exemplary in nature and shouldnot be considered limiting in any way. In that regard, it is understoodthat any communication pathway between the instrument 175 and thecomputing device 172 may be utilized, including physical connections(including electrical, optical, and/or fluid connections), wirelessconnections, and/or combinations thereof. In that regard, it isunderstood that the connection 178 is wireless in some instances. Insome instances, the connection 178 includes a communication link over anetwork (e.g., intranet, internet, telecommunications network, and/orother network). In that regard, it is understood that the computingdevice 172 is positioned remote from an operating area where theinstrument 175 is being used in some instances. Having the connection178 include a connection over a network can facilitate communicationbetween the instrument 175 and the remote computing device 172regardless of whether the computing device is in an adjacent room, anadjacent building, or in a different state/country. Further, it isunderstood that the communication pathway between the instrument 175 andthe computing device 172 is a secure connection in some instances.Further still, it is understood that, in some instances, the datacommunicated over one or more portions of the communication pathwaybetween the instrument 175 and the computing device 172 is encrypted.

It is understood that one or more components of the system 150 are notincluded, are implemented in a different arrangement/order, and/or arereplaced with an alternative device/mechanism in other embodiments ofthe present disclosure. For example, in some instances, the system 150does not include interface 170 and/or interface 176. In such instances,the connector 168 (or other similar connector in communication withinstrument 152 or instrument 175) may plug into a port associated withcomputing device 172. Alternatively, the instruments 152, 175 maycommunicate wirelessly with the computing device 172. Generallyspeaking, the communication pathway between either or both of theinstruments 152, 175 and the computing device 172 may have nointermediate nodes (i.e., a direct connection), one intermediate nodebetween the instrument and the computing device, or a plurality ofintermediate nodes between the instrument and the computing device.

Referring now to FIGS. 5-8, shown therein are graphical representationsof diagnostic information illustrating aspects of an embodiment of thepresent disclosure. In that regard, FIG. 5 is a graphical representationof measured pressure, velocity, and resistance within a vessel; FIG. 6is a magnified view of a portion of the graphical representation of FIG.5 corresponding to a resting state of a patient; FIG. 7 is a magnifiedview of a portion of the graphical representation of FIG. 5corresponding to a hyperemic state of a patient; and FIG. 8 is theportion of the graphical representation of FIG. 6 annotated to identifya diagnostic window according to an embodiment of the presentdisclosure.

Referring more particularly to FIG. 5, shown therein is a graphicalrepresentation 180 of diagnostic information pertaining to a vessel.More specifically, the graphical representation 180 includes a graph 182plotting pressure within the vessel over time, a graph 184 plottingvelocity of the fluid within the vessel over time, and a graph 186plotting resistance within the vessel over time. In that regard, theresistance (or impedance) shown in graph 186 is calculated based on thepressure and velocity data of graphs 182 and 184. In particular, theresistance values shown in graph 186 are determined by dividing thepressure measurement of graph 182 by the velocity measurement 184 forthe corresponding point in time. The graphical representation 180includes a time period 188 that corresponds to a resting state of thepatient's heart and a time period 190 that corresponds to a stressedstate of the patient's heart. In that regard, the stressed state of thepatient's heart is caused by the administration of a hyperemic agent insome instances.

To better illustrate the differences in the pressure, velocity, andresistance data between the resting and stressed states of the patient,close-up views of the data within windows 192 and 194 are provided inFIGS. 6 and 7. Referring more specifically to FIG. 6, window 192 of thegraphical representation 180 includes graph portions 196, 198, and 200that correspond to graphs 182, 184, and 186, respectively. As shown, inthe resting state of FIG. 6, the resistance within the vessel has anaverage value of approximately 0.35 on the scale of graph 200, asindicated by line 202. Referring now to FIG. 7, window 194 of thegraphical representation 180 includes graph portions 204, 206, and 208that correspond to graphs 182, 184, and 186, respectively. As shown, inthe stressed state of FIG. 7, the resistance within the vessel issignificantly less than the resting state with a value of approximately0.20 on the scale of graph 208, as indicated by line 210. As current FFRtechniques rely on the average pressures across an entire heartbeatcycle, it is necessary to stress the patient's heart to achieve thisreduced and relatively constant resistance across the entire heartbeatso that the data obtained is suitable for use with FFR techniques.

Referring to FIG. 8, similar to FIG. 6 window 192 of the graphicalrepresentation 180 of FIG. 5 is shown and includes graph portions 196,198, and 200 that correspond to graphs 182, 184, and 186, respectively.However, in FIG. 8 a section 212 of the heartbeat cycle of the patienthas been identified. As shown, section 212 corresponds to the portion ofthe heartbeat cycle of the patient where the resistance is reducedwithout the use of a hyperemic agent or other stressing technique. Thatis, section 212 is a portion of the heartbeat cycle of a resting patientthat has a naturally reduced and relatively constant resistance. Inother instances, section 212 of the heartbeat cycle encompasses theportion the heartbeat cycle that is less than a fixed percentage of themaximum resistance of the heartbeat cycle. In that regard, the fixedpercentage of the maximum resistance of the heartbeat cycle is less than50%, less than 30%, less than 25%, less than 20%, less than 15%, lessthan 10%, and less than 5% in some embodiments. In yet other instances,section 212 of the heartbeat cycle encompasses the portion the heartbeatcycle that is less than a fixed percentage of the average resistance ofthe heartbeat cycle. In that regard, the fixed percentage of the averageresistance of the heartbeat cycle is less than 75%, less than 50%, lessthan 25%, less than 20%, less than 15%, less than 10%, and less than 5%in some embodiments.

Accordingly, in some embodiments of the present disclosure, the portionof the heartbeat cycle coinciding with section 212 is utilized as adiagnostic window for evaluating a stenosis of the vessel of a patientwithout the use of a hyperemic agent or other stressing of the patient'sheart. In particular, the pressure ratio (distal pressure divided byproximal pressure) across the stenosis is calculated for the time periodcorresponding to section 212 for one or more heartbeats. The calculatedpressure ratio is an average over the diagnostic window defined bysection 212 in some instances. By comparing the calculated pressureratio to a threshold or predetermined value, a physician or othertreating medical personnel can determine what, if any, treatment shouldbe administered. In that regard, in some instances, a calculatedpressure ratio above a threshold value (e.g., 0.80 on a scale of 0.00 to1.00) is indicative of a first treatment mode (e.g., no treatment, drugtherapy, etc.), while a calculated pressure ratio below the thresholdvalue is indicative of a second, more invasive treatment mode (e.g.,angioplasty, stent, etc.). In some instances, the threshold value is afixed, preset value. In other instances, the threshold value is selectedfor a particular patient and/or a particular stenosis of a patient. Inthat regard, the threshold value for a particular patient may be basedon one or more of empirical data, patient characteristics, patienthistory, physician preference, available treatment options, and/or otherparameters.

In some instances, section 212 is identified by monitoring pressure andfluid flow velocity within the vessel using one or more instruments andcalculating the resistance within the vessel based on the measuredpressure and velocity. For example, referring again to the embodiment ofFIG. 3, in some instances the instrument 130 includes one or moresensing elements configured to monitor at least pressure and flowvelocity, while instrument 132 includes one or more sensing elementsconfigured to monitor at least pressure. Accordingly, with the one ormore sensing elements of instrument 130 positioned distal of thestenosis and the one or more sensing elements of instrument 132positioned proximal of the stenosis, the pressure and flow velocitymeasurements obtained by instrument 130 are utilized to identify section212. Based on the identification of section 212, then the correspondingdistal pressure measurements (as obtained by the one or more sensingelements of instrument 130) are compared to the proximal pressuremeasurements (as obtained by the one or more sensing elements ofinstrument 132) to calculate the pressure ratio across the stenosisduring the diagnostic window defined by section 212. Additional examplesof evaluating a vessel based on pressure and flow velocity measurementsare described in UK Patent Application No. 1003964.2 filed Mar. 10, 2010and titled “METHOD AND APPARATUS FOR THE MEASUREMENT OF A FLUID FLOWRESTRICTION IN A VESSEL”, which is hereby incorporated by reference inits entirety.

In other instances, section 212 is identified without monitoring fluidvelocity. In that regard, several techniques for identifying suitablediagnostic windows for use in evaluating a stenosis of a vessel based onpressure ratio across the stenosis without the use of hyperemic agentsare described below. In some instances, the diagnostic window isidentified solely based on characteristics of the pressure measurementsobtained by instruments positioned within the vessel. Accordingly, insuch instances, the instruments utilized need only have elementsconfigured to monitor a pressure within the vessel, which results inreduced cost and simplification of the system. Exemplary techniques forevaluating a vessel based on pressure measurements are described in UKPatent Application No. 1100137.7 filed Jan. 6, 2011 and titled“APPARATUS AND METHOD OF ASSESSING A NARROWING IN A FLUID FILLED TUBE”,which is hereby incorporated by reference in its entirety.

In general, the diagnostic window for evaluating differential pressureacross a stenosis without the use of a hyperemic agent in accordancewith the present disclosure may be identified based on characteristicsand/or components of one or more of proximal pressure measurements,distal pressure measurements, proximal velocity measurements, distalvelocity measurements, ECG waveforms, and/or other identifiable and/ormeasurable aspects of vessel performance. In that regard, various signalprocessing and/or computational techniques can be applied to thecharacteristics and/or components of one or more of proximal pressuremeasurements, distal pressure measurements, proximal velocitymeasurements, distal velocity measurements, ECG waveforms, and/or otheridentifiable and/or measurable aspects of vessel performance to identifya suitable diagnostic window.

In some embodiments, the determination of the diagnostic window and/orthe calculation of the pressure differential are performed inapproximately real time or live to identify the section 212 andcalculate the pressure ratio. In that regard, calculating the pressureratio in “real time” or “live” within the context of the presentdisclosure is understood to encompass calculations that occur within 10seconds of data acquisition. It is recognized, however, that often “realtime” or “live” calculations are performed within 1 second of dataacquisition. In some instances, the “real time” or “live” calculationsare performed concurrent with data acquisition. In some instances thecalculations are performed by a processor in the delays between dataacquisitions. For example, if data is acquired from the pressure sensingdevices for 1 ms every 5 ms, then in the 4 ms between data acquisitionsthe processor can perform the calculations. It is understood that thesetimings are for example only and that data acquisition rates, processingtimes, and/or other parameters surrounding the calculations will vary.In other embodiments, the pressure ratio calculation is performed 10 ormore seconds after data acquisition. For example, in some embodiments,the data utilized to identify the diagnostic window and/or calculate thepressure ratio are stored for later analysis.

Referring now to FIGS. 9-11, shown therein are graphical representationsof diagnostic information illustrating aspects of another embodiment ofthe present disclosure. In that regard, FIG. 9 is a graphicalrepresentation of measured pressure and velocity within a vessel; FIG.10 is a graphical representation of a differential of the measuredvelocity of FIG. 9; and FIG. 11 is the graphical representation ofmeasured pressure and velocity within the vessel annotated to identify adiagnostic window according to an embodiment of the present disclosure.

Referring more specifically to FIG. 9, graphical representation 220includes a plot 222 representative of pressure (measured in mmHg) withina vessel over the time period of one cardiac cycle and a plot 224representative of velocity (measured in m/s) of a fluid within thevessel over the same cardiac cycle. FIG. 10, in turn, is a graphicalrepresentation 230 of a differential of the velocity plot 224 ofgraphical representation 220 of FIG. 9. In that regard, in someinstances, the velocity differential or change in velocity (dU) iscalculated as

${{dU}_{xy} = \frac{U_{x} - U_{y}}{t}},$

where U_(x) is the velocity at time x, U_(y) is the velocity at time y,and t is the elapsed time between U_(x) and U_(y). In some instances,the variable t is equal to the sample rate of the velocity measurementsof the system such that the differential is calculated for all datapoints. In other instances, the variable t is longer than the samplerate of the velocity measurements of the system such that only a subsetof the obtained data points are utilized.

As shown in FIG. 10, for a time period 232 extending from about 625 msto about 1000 ms the differential of the velocity plot 224 is relativelystabilized around zero. In other words, the velocity of the fluid withinthe vessel and/or the vascular resistance is relatively constant duringtime period 232. In some instances, the velocity is consideredstabilized when it varies between −0.01 and +0.01, and in some specificinstance is considered stabilized when it varies between about −0.005and about +0.005. However, in other instances, the velocity isconsidered stabilized with values outside of these ranges. Similarly,for a time period 234 extending from about 200 ms to about 350 ms thedifferential of the velocity plot 224 is relatively stabilized aroundzero representing that the velocity of the fluid within the vessel issubstantially constant during time period 234 as well. However, timeperiod 234 can be highly variable, as valvular disease, dyssynchronywithin a ventricle, regional myocardial contractile differences,microvascular disease can all lead to large variations of timing of thetime period 234. As discussed below, all or portions of the time periods232 and/or 234 are utilized as a diagnostic window for evaluatingpressure ratio across a stenosis in some embodiments of the presentdisclosure. In that regard, the diagnostic window is selected byidentifying a portion of the cardiac cycle corresponding to the timeperiod in which the change in velocity (i.e., dU) fluctuates aroundzero. FIG. 11 shows the graphical representation 220 of FIG. 9 annotatedto identify a diagnostic window 236 corresponding to the time period 232of FIG. 10. In other instances, the diagnostic window is selected byidentifying a portion of the cardiac cycle corresponding to a period inwhich the change in velocity (i.e., dU) is relatively small compared tothe maximum change in velocity (i.e., dU_(max)) during a cardiac cycle.In the illustrated embodiment of FIG. 10, the maximum change in velocity(i.e., dU_(max)) occurs at point 235. In some instances, the diagnosticwindow is selected by identifying the portion(s) of the cardiac cyclewhere the change in velocity (i.e., dU) is less than 25%, less than 20%,less than 15%, less than 10%, and/or less than 5% of the maximum changein velocity (i.e., dU_(max)) for the cardiac cycle.

There are a variety of signal processing techniques that can be utilizedto identify time period 232, time period 234, and/or other time periodswhere the change in velocity is relatively constant and approximatelyzero, such as variation or standard deviation from the mean, minimumthreshold offset, or otherwise. Further, while time periods 232 and 234have been identified using a differential of the velocity measurement,in other instances first, second, and/or third derivatives of thevelocity measurement are utilized. For example, identifying time periodsduring the cardiac cycle where the first derivative of velocity isrelatively constant and approximately zero allows the localization oftime periods where velocity is relatively constant. Further, identifyingtime periods during the cardiac cycle where the second derivative ofvelocity is relatively constant and approximately zero allows thelocalization of a time period where acceleration is relatively constantand near zero, but not necessarily zero.

Time periods 232, 234, and/or other time periods where the change invelocity is relatively constant and approximately zero (i.e., the speedof the fluid flow is stabilized) are suitable diagnostic windows forevaluating a pressure differential across a stenosis of a vessel withoutthe use of a hyperemic agent in accordance with the present disclosure.In that regard, in a fluid flow system, the separated forward andbackward generated pressures are defined by:

${{dP}_{+} = {{\frac{1}{2}( {{dP} + {\rho \; {cd}\; U}} )\mspace{14mu} {and}\mspace{14mu} {dP}_{-}} = {\frac{1}{2}( {{dP} - {\rho \; {cd}\; U}} )}}},$

where dP is the differential of pressure, p is the density of the fluidwithin the vessel, c is the wave speed, and dU is the differential offlow velocity. However, where the flow velocity of the fluid issubstantially constant, dU is approximately zero and the separatedforward and backward generated pressures are defined by:

${dP}_{+} = {{\frac{1}{2}( {{dP} + {\rho \; {c(0)}}} )} = {{\frac{1}{2}{dP}\mspace{14mu} {and}\mspace{14mu} {dP}_{-}} = {{\frac{1}{2}( {{dP} - {\rho \; {c(0)}}} )} = {\frac{1}{2}{{dP}.}}}}}$

In other words, during the time periods where dU is approximately zero,the forward and backward generated pressures are defined solely bychanges in pressure.

Accordingly, during such time periods the severity of a stenosis withinthe vessel can be evaluated based on pressure measurements takenproximal and distal of the stenosis. In that regard, by comparing theforward and/or backward generated pressure distal of a stenosis to theforward and/or backward generated pressure proximal of the stenosis, anevaluation of the severity of the stenosis can be made. For example, theforward-generated pressure differential can be calculated as

$\frac{P_{+ {distal}}}{P_{+ {proximal}}},$

while the backward-generated pressure differential can be calculated as

$\frac{P_{- {distal}}}{P_{- {proximal}}}.$

In the context of the coronary arteries, a forward-generated pressuredifferential is utilized to evaluate a stenosis in some instances. Inthat regard, the forward-generated pressure differential is calculatedbased on proximally originating (i.e., originating from the aorta)separated forward pressure waves and/or reflections of the proximallyoriginating separated forward pressure waves from vascular structuresdistal of the aorta in some instances. In other instances, abackward-generated pressure differential is utilized in the context ofthe coronary arteries to evaluate a stenosis. In that regard, thebackward-generated pressure differential is calculated based on distallyoriginating (i.e., originating from the microvasculature) separatedbackward pressure waves and/or reflections of the distally originatingseparated backward pressure waves from vascular structures proximal ofthe microvasculature.

In yet other instances, a pressure wave is introduced into the vessel byan instrument or medical device. In that regard, the instrument ormedical device is utilized to generate a proximally originating forwardpressure wave, a distally originating backward pressure wave, and/orcombinations thereof for use in evaluating the severity of the stenosis.For example, in some embodiments an instrument having a movable membraneis positioned within the vessel. The movable membrane of the instrumentis then activated to cause movement of the membrane and generation of acorresponding pressure wave within the fluid of the vessel. Based on theconfiguration of the instrument, position of the membrane within thevessel, and/or the orientation of the membrane within the vessel thegenerated pressure wave(s) will be directed distally, proximally, and/orboth. Pressure measurements based on the generated pressure wave(s) canthen be analyzed to determine the severity of the stenosis.

Referring now to FIGS. 12-15, shown therein are graphicalrepresentations of diagnostic information illustrating aspects ofanother embodiment of the present disclosure. In that regard, FIG. 12 isa graphical representation of wave intensity within a vessel; FIG. 13 isa graphical representation of proximal and distal originating pressurewaves within the vessel corresponding to the wave intensity of FIG. 12;FIG. 14 is a graphical representation of pressure and velocity withinthe vessel corresponding to the wave intensity of FIG. 12 and theproximal and distal originating pressure waves of FIG. 13; and FIG. 15is a graphical representation of a resistance within the vesselcorresponding to the wave intensity of FIG. 12, the proximal and distaloriginating pressure waves of FIG. 13, and the pressure and velocity ofFIG. 14.

Referring more specifically to FIG. 12, shown therein is a graphicalrepresentation 240 plotting the intensities associated with proximallyand distally originating waves of a cardiac cycle over time. In thatregard, plot 242 is representative of proximally originating waves,while plot 244 is representative of distally originating waves. Asshown, six predominating waves are associated with the cardiac cycle ofa patient. In order of occurrence during a cardiac cycle, wave 246 is abackward-traveling pushing wave, wave 248 is a dominantforward-traveling pushing wave, wave 250 is a backward-traveling pushingwave, wave 252 is a forward-traveling suction wave, wave 254 is adominant backward-traveling suction wave, and wave 256 is aforward-traveling pushing wave. Notably, no waves are generated during atime period 258 late in the cardiac cycle. In some instances, the timeperiod 258 is referred to as a wave-free period of the cardiac cycle.Additional details regarding pressure waves in the context of thecoronary arteries can be found in “Evidence of a DominantBackward-Propagating ‘Suction’ Wave Responsible for Diastolic CoronaryFilling in Humans, Attenuated in Left Ventricular Hypertrophy” by Davieset al. (Circulation. 2006; 113:1768-1778), which is hereby incorporatedby reference in its entirety.

Referring now to FIG. 13, shown therein is a graphical representation260 of proximal and distal originating pressure waves within a vesselover a time period associated with a cardiac cycle. In that regard, thepressure waves of FIG. 13 correspond to the wave intensities of FIG. 12.As shown, the graphical representation 260 includes a plot 262representative of a proximally-originating pressure, a plot 264representative of a distally-originating pressure, and a plot 265representative of the total pressure (proximally-originating pressureplus the distally-originating pressure).

Referring now to FIG. 14, shown therein is a graphical representation270 that includes a plot 272 representative of pressure (measured inmmHg) within a vessel over time and a plot 274 representative ofvelocity (measured in cm/s) of a fluid within the vessel over time. Inthat regard, the pressure and velocity plots 272, 274 of FIG. 14correspond to the wave intensities and pressure waves of FIGS. 12 and13, respectively. As shown, for the wave-free time period 258 extendingfrom about 475 ms to about 675 ms the slopes of the pressure plot 272and the velocity plot 274 are relatively constant. At this time point,as shown in FIG. 15, the resistance within the vessel is relativelyconstant and reduced during the time period 258. In that regard, thegraphical representation 280 of FIG. 15 includes a plot 282 of theresistance within the vessel over the time of a cardiac cycle. In thatregard, the resistance values of graphical representation 280 arecalculated using the pressure and velocity measurements of FIG. 14,where resistance is equal to pressure divided by velocity for aparticular point in time along the cardiac cycle. Due to the reduced andrelative constant resistance during time period 258, all or a portion ofthe time period 258 is suitable for use as a diagnostic window forevaluating pressure differential across a stenosis in some embodimentsof the present disclosure. In that regard, in some embodiments thediagnostic window is the period of minimum resistance that correspondsto the wave-free period at the end of the backward-travelling suctionwave, running to shortly before the end of the cardiac cycle.

Referring now to FIGS. 16-26, shown therein are various graphicalrepresentations of techniques for determining start and/or end pointsfor a diagnostic window in accordance with the present disclosure. Inthat regard, FIGS. 16-18 generally illustrate identification of astarting point of a diagnostic window based on a proximal pressuremeasurement; FIGS. 19-22 generally illustrate identification of astarting point of a diagnostic window based on a distal pressuremeasurement; FIG. 23 illustrates identification of an end of adiagnostic window based on a starting point of the diagnostic window;FIG. 24 illustrates identification of an ending point of a diagnosticwindow based on a proximal pressure measurement; and FIGS. 25 and 26illustrate identification of an ending point of a diagnostic windowbased on a distal pressure measurement.

As shown in FIG. 16, a graphical representation 300 includes a proximalpressure reading 302 and a distal pressure reading 304 each plotted overtime relative to a cardiac cycle. In that regard, the proximal pressurereading 302 is representative of a pressure proximal of a stenosis of avessel. The proximal pressure reading 302 is based upon a partialpressure (e.g., forward generated or backward generated) in someinstances. Similarly, the distal pressure reading 304 is representativeof a pressure distal of the stenosis. The distal pressure reading 304 isbased upon a partial pressure (e.g., forward generated or backwardgenerated) in some instances.

For simplicity and consistency, the proximal and distal pressurereadings 302 and 304 provided in FIG. 16 will be utilized in describingthe techniques associated with FIGS. 17-28 as well. However, withrespect to all of the disclosed techniques the proximal and distalpressure readings 302 and 304 are exemplary and should not be consideredlimiting in any way. In that regard, it is understood that the pressurereadings will vary from patient to patient and even between cardiaccycles of a single patient. Accordingly, it is understood that thetechniques described herein for identifying a diagnostic window based onthese pressure readings are suitable for use with a wide variety ofpressure reading plots. Further, it is understood that the techniquesdescribed below are calculated or determined over a plurality of cardiaccycles in some instances. For example, in some embodiments thediagnostic window is identified by making calculations over a pluralityof cardiac cycles and calculating an average or mean value, identifyingoverlapping areas common to the plurality of cardiac cycles, and/orotherwise identifying a suitable time period for a diagnostic window.Further still, it is understood that two or more of the techniquesdescribed below may be utilized together to identify a starting point,ending point, and/or other aspect of a diagnostic window.

Referring now to FIGS. 16-18, shown therein are several techniques foridentifying a starting point of a diagnostic window based on a proximalpressure measurement. Referring more specifically to FIG. 16, thestarting point of the diagnostic window is determined by identifying adicrotic notch and adding a fixed amount of time in some instances. Asshown in FIG. 16, a dicrotic notch 306 has been identified and a fixedtime period 308 has been added to determine the starting point 310 of adiagnostic window. The fixed time period 308 is between about 1 ms andabout 500 ms in some instances. In some particular instances, the timeperiod 308 is between about 25 ms and about 150 ms. In other instances,the amount of time added to the start of diastole is selected based on apercentage of the cardiac cycle or a percentage of the length ofdiastole. For example, in some instances, the amount of time added isbetween about 0% and about 70% of the length of the cardiac cycle. Inyet other instances, no time is added to the dicrotic notch, such thatthe dicrotic notch 306 is the starting point 310.

In another embodiment, a start of diastole is identified based on theproximal pressure measurements and a fixed time period is added todetermine the starting point of a diagnostic window. The fixed timeperiod is between about 1 ms and about 500 ms. In some particularembodiments, the fixed time period is between the beginning of diastoleand the start of the diagnostic window is between about 25 ms and about200 ms. In other instances, the amount of time added to the start ofdiastole is selected based on a percentage of the cardiac cycle or apercentage of the length of diastole. For example, in some instances,the time added to the start of diastole is between about 0% and about70% of the cardiac cycle. In other instances, the time added to thestart of diastole is between about 0% and about 100% of the total lengthof the diastole portion of the cardiac cycle. In some instances, thetime added to the start of diastole is between about 2% and about 75% ofthe total length of the diastole portion of the cardiac cycle. In yetother instances, no time is added to the start of diastole, such thatthe start of diastole is also the starting point of the diagnosticwindow.

Referring now to FIG. 17, the starting point of the diagnostic window isdetermined by identifying a peak proximal pressure and adding a fixedamount of time in some instances. As shown in the graphicalrepresentation 312 of FIG. 17, a peak pressure 314 has been identifiedand a fixed time period 316 has been added to determine the startingpoint 318 of a diagnostic window. The fixed time period 316 is betweenabout 1 ms and about 550 ms in some instances. In some instances, thefixed time period 316 is between about 25 ms and about 175 ms. In otherinstances, the amount of time added to the peak proximal pressure isselected based on a percentage of the cardiac cycle or a percentage ofthe length of diastole. For example, in some instances, the amount oftime added is between about 0% and about 70% of the length of thecardiac cycle. In yet other instances, no time is added to the peakproximal pressure, such that the peak pressure 314 is the starting point318.

Referring now to FIG. 18, the starting point of the diagnostic window isdetermined by identifying the start of a cardiac cycle and adding afixed amount of time in some instances. As shown in the graphicalrepresentation 320 of FIG. 18, a start 322 of the cardiac cycle has beenidentified and a fixed time period 324 has been added to determine thestarting point 326 of a diagnostic window. The fixed time period 324 isbetween about 150 ms and about 900 ms in some instances. In someinstances, the fixed time period 324 is between about 300 ms and about600 ms. In some particular embodiments, the fixed time period 324 iscalculated as a percentage of the length 328 of a cardiac cycle of thepatient. As shown in FIG. 18, an end 330 of the cardiac cycle has beenidentified such that the length 328 of the cardiac cycle extends betweenthe start 322 and the end 330. The percentage of the length 328 of thecardiac cycle utilized for calculating the starting point 356 is betweenabout 25% and about 95% in some instances. In some instances, thepercentage of the length 328 of the cardiac cycle is between about 40%and about 75%. In yet other instances, no time is added to the start ofthe cardiac cycle, such that the start of the cardiac cycle 322 is thestarting point 326.

Referring now to FIGS. 19-22, shown therein are several techniques foridentifying a starting point of a diagnostic window based on a distalpressure measurement. Referring more specifically to FIG. 19, thestarting point of the diagnostic window is determined by identifying adicrotic notch and adding a fixed amount of time in some instances. Asshown in the graphical representation 332 of FIG. 19, a dicrotic notch334 has been identified and a fixed time period 336 has been added todetermine the starting point 338 of a diagnostic window. The fixed timeperiod 336 is between about 1 ms and about 500 ms in some instances. Insome instances, the fixed time period 336 is between about 25 ms andabout 150 ms. In other instances, a peak pressure 339 is identifiedbased on the distal pressure measurements and a fixed time period isadded to determine the starting point of a diagnostic window. The fixedtime period relative to the peak pressure is between about 1 ms andabout 550 ms in some instances. In some instances, the fixed time periodis between about 25 ms and about 175 ms. In yet other instances, no timeis added to the dicrotic notch, such that the dicrotic notch 334 is thestarting point 338.

In another embodiment, a start of diastole is identified based on thedistal pressure measurements and a fixed time period is added todetermine the starting point of a diagnostic window. The fixed timeperiod is between about 1 ms and about 500 ms. In some particularembodiments, the fixed time period between the beginning of diastole andthe start of the diagnostic window is between about 25 ms and about 200ms. In other instances, the amount of time added to the start ofdiastole is selected based on a percentage of the cardiac cycle or apercentage of the length of diastole. For example, in some instances,the time added to the start of diastole is between about 0% and about70% of the cardiac cycle. In other instances, the time added to thestart of diastole is between about 0% and about 100% of the total lengthof the diastole portion of the cardiac cycle. In some instances, thetime added to the start of diastole is between about 2% and about 75% ofthe total length of the diastole portion of the cardiac cycle. In yetother instances, no time is added to the start of diastole, such thatthe start of diastole is the starting point of the diagnostic window.

Referring now to FIG. 20, the starting point of the diagnostic window isdetermined by identifying a maximum change in pressure and adding afixed amount of time in some instances. In some particular instances,the maximum change in pressure after a peak distal pressure is utilizedas the basis point from which the fixed amount of time is added. Asshown in the graphical representation 340 of FIG. 20, after peakpressure 342 the point having a maximum change in pressure (i.e., dP/dt)is identified by point 344. A fixed time period 346 has been added topoint 344 to determine the starting point 348 of a diagnostic window.The fixed time period 346 is between about 1 ms and about 500 ms in someinstances. In some instances, the fixed time period 346 is between about25 ms and about 150 ms. In some particular embodiments, the fixed timeperiod 346 is calculated as a percentage of the length of the cardiaccycle of the patient. The percentage of the length of the cardiac cycleutilized for calculating the starting point 348 is between about 0% andabout 70% in some instances. In yet other instances, no time is added tothe point 344 representative of the maximum change in pressure, suchthat the point 344 is the starting point 348.

Referring now to FIG. 21, the starting point of the diagnostic window isdetermined by identifying the start of a cardiac cycle and adding afixed amount of time in some instances. As shown in the graphicalrepresentation 350 of FIG. 21, a start 352 of the cardiac cycle has beenidentified and a fixed time period 354 has been added to determine thestarting point 356 of a diagnostic window. The fixed time period 354 isbetween about 150 ms and about 900 ms in some instances. In someinstances, the fixed time period 354 is between about 300 ms and about600 ms. In some particular embodiments, the fixed time period 354 iscalculated as a percentage of the length 358 of the cardiac cycle of thepatient. As shown in FIG. 21, an end 360 of the cardiac cycle has beenidentified such that the length 358 of the cardiac cycle extends betweenthe start 352 and the end 360. The percentage of the length 358 of thecardiac cycle utilized for calculating the starting point 356 is betweenabout 25% and about 95% in some instances. In some particular instances,the percentage of the length 358 of the cardiac cycle is between about40% and about 75%. In yet other instances, no time is added to the startof the cardiac cycle, such that the start of the cardiac cycle 352 isthe starting point 356.

Referring now to FIG. 22, the starting point of the diagnostic window isdetermined by identifying a ventricularization point in some instances.As shown in the graphical representation 362 of FIG. 22, aventricularization point 364 of the cardiac cycle has been identified.In some instances, the ventricularization point 364 is identified basedon the change in slope of the distal pressure reading. In theillustrated embodiment, the starting point 366 of the diagnostic windowsubstantially coincides with the ventricularization point 364. In otherinstances, the starting point 366 is set to be a fixed amount of timebefore or after the ventricularization point. In that regard, the fixedtime period is between about −250 ms and about 400 ms in some instances.In some instances, the fixed time period is between about −50 ms andabout 100 ms.

Referring now to FIG. 23, shown therein is a graphical representation370 illustrating a technique for identifying an ending point of adiagnostic window based on a starting point 372 of the diagnosticwindow. As shown, the diagnostic window has an ending point 374 that isspaced from the starting point 372 by a fixed amount of time 376. Thefixed time period 376 is between about 1 ms and about 700 ms in someinstances. In some instances, the fixed time period 376 is between about200 ms and about 500 ms. In some particular embodiments, the fixed timeperiod 376 is calculated as a percentage of the length of the cardiaccycle of the patient. The percentage of the length of the cardiac cycleutilized for calculating the time period 376 is between about 0% andabout 70% in some instances. In some instances, the percentage of thelength of the cardiac cycle is between about 25% and about 50%. In otherinstances, the diagnostic window is a specific point in the cardiaccycle such that time 376 is zero. In that regard, the techniquesdescribed for identifying the starting point and/or the ending point ofa diagnostic window are suitable for identifying such a diagnostic pointin the cardiac cycle for evaluating pressure differential. In someinstances, a diagnostic window for a single cardiac cycle is comprisedof a plurality of discrete diagnostic points along the single cardiaccycle.

Referring now to FIG. 24, shown therein is a graphical representation380 illustrating a technique for identifying an ending point of adiagnostic window based on identifying the end of a cardiac cycleaccording to a proximal pressure measurement, which is an aorticpressure measurement in some instances, and subtracting a fixed amountof time. As shown, an end 382 of the cardiac cycle has been identifiedand a fixed time period 384 has been subtracted to determine the endingpoint 386 of a diagnostic window. The fixed time period 384 is betweenabout 1 ms and about 600 ms in some instances. In some particularembodiments, the fixed time period 384 is calculated as a percentage ofthe length of the cardiac cycle of the patient. The percentage of thelength of the cardiac cycle utilized for calculating the time period 384is between about 0% and about 70% in some instances. In some instances,the percentage of the length of the cardiac cycle is between about 1%and about 25%. In yet other instances, no time is subtracted from theend of the cardiac cycle, such that the end of the cardiac cycle 382 isthe ending point 386.

Referring now to FIGS. 25 and 26, shown therein are techniques foridentifying an ending point of a diagnostic window based on a distalpressure measurement. Referring more specifically to FIG. 25, showntherein is a graphical representation 390 illustrating a technique foridentifying an ending point of a diagnostic window based on identifyingthe end of a cardiac cycle according to a distal pressure measurementand subtracting a fixed amount of time. As shown, an end 392 of thecardiac cycle has been identified and a fixed time period 394 has beensubtracted to determine the ending point 396 of a diagnostic window. Thefixed time period 394 is between about 1 ms and about 600 ms. In someinstances, the fixed time period 394 is between about 5 ms and about 100ms. In some particular embodiments, the fixed time period 394 iscalculated as a percentage of the length of the cardiac cycle of thepatient. The percentage of the length of the cardiac cycle utilized forcalculating the time period 394 is between about 0% and about 70%. Insome instances, the percentage of the length of the cardiac cycle isbetween about 1% and about 25%. In yet other instances, no time issubtracted from the end of the cardiac cycle, such that the end of thecardiac cycle 392 is the ending point 396.

Referring to FIG. 26, shown therein is a graphical representation 400illustrating a technique for identifying an ending of a diagnosticwindow based on identifying the ventricularization point of a distalpressure measurement. As shown, a ventricularization point 402 of thecardiac cycle has been identified. In some instances, theventricularization point 402 is identified based on the change in slopeof the distal pressure reading. In the illustrated embodiment, an endingpoint 404 of the diagnostic window substantially coincides with theventricularization point 402. In other instances, the ending point 404is set to be a fixed amount of time before or after theventricularization point. In that regard, the fixed time period isbetween about −200 ms and about 450 ms. In some instances, the fixedtime period is between about −50 ms and about 100 ms.

Referring now to FIGS. 27 and 28, shown therein are graphicalrepresentations of exemplary diagnostic windows relative to proximal anddistal pressure measurements. In that regard, FIG. 27 illustrates adiagnostic window that begins shortly after ventricularization, whileFIG. 28 illustrates a diagnostic window that begins beforeventricularization.

Referring more specifically to FIG. 27, graphical representation 410shows a diagnostic window 412 that includes a starting point 414 and anending point 416. In some instances, the starting point 414 is selectedusing one or more of the techniques described above for identifying astarting point of a diagnostic window. Similarly, in some instances, theending point 416 is selected using one or more of the techniquesdescribed above for identifying an ending point of a diagnostic window.As shown, the diagnostic window 412 begins after the ventricularizationpoint of the distal pressure reading 304 and ends before the end of thecardiac cycle.

Referring now to FIG. 28, graphical representation 420 shows adiagnostic window 422 that includes a starting point 424 and an endingpoint 426. In some instances, the starting point 424 is selected usingone or more of the techniques described above for identifying a startingpoint of a diagnostic window. Similarly, in some instances, the endingpoint 426 is selected using one or more of the techniques describedabove for identifying an ending point of a diagnostic window. As shown,the diagnostic window 422 begins before the ventricularization point ofthe distal pressure reading 304 and ends before the end of the cardiaccycle such that the ventricularization point is included within thediagnostic window 422.

Referring now to FIG. 29, shown therein is graphical representation ofan ECG signal annotated with exemplary diagnostic windows accordingembodiments of the present disclosure. Generally, at least oneidentifiable feature of the ECG signal (including without limitation,the start of a P-wave, the peak of a P-wave, the end of a P-wave, a PRinterval, a PR segment, the beginning of a QRS complex, the start of anR-wave, the peak of an R-wave, the end of an R-wave, the end of a QRScomplex (J-point), an ST segment, the start of a T-wave, the peak of aT-wave, and the end of a T-wave) is utilized to select that startingpoint and/or ending point of the diagnostic window. For example, in someinstances, a diagnostic window is identified using the decline of theT-wave as the starting point and the start of the R-wave as the endingpoint. In some instances, the starting point and/or ending point of thediagnostic window is determined by adding a fixed amount of time to anidentifiable feature of the ECG signal. In that regard, the fixed amounttime is a percentage of the cardiac cycle in some instances.

Referring now to FIG. 30, shown therein is a graphical representation450 of a proximal pressure 452 and a distal pressure 454 over a seriesof cardiac cycles of a patient. In that regard, a diagnostic window 456has been identified that includes a starting point 458 and an endingpoint 460 for a cardiac cycle 462. The diagnostic window 456 is definedby the starting point 458 and the ending point 460. In the illustratedembodiment, the starting point 458 is selected to be positioned at afixed percentage of the total diastole time of the cardiac cycle 462after a maximum decline in pressure. In some instances, the fixedpercentage of the total diastole time added to the point of maximumpressure decline to determine the starting point 458 is between about10% and about 60%, with some particular embodiments having a percentagebetween about 20% and about 30%, and with one particular embodimenthaving a percentage of about 25%. The ending point 560 is selected to bepositioned at a fixed percentage of the total diastole time or diastolicwindow from the beginning of diastole for the cardiac cycle 462. In someinstances, the fixed percentage of the total diastole time added to thebeginning of diastole to determine the ending point 460 is between about40% and about 90%, with some particular embodiments having a percentagebetween about 60% and about 80%, and with one particular embodimenthaving a percentage of about 70%. In other embodiments, the ending point560 is selected to be positioned at a fixed percentage of the totaldiastole time or diastolic window from the end of diastole for thecardiac cycle 462. In some instances, the fixed percentage of the totaldiastole time subtracted from the end of diastole to determine theending point 460 is between about 10% and about 60%, with someparticular embodiments having a percentage between about 20% and about40%, and with one particular embodiment having a percentage of about30%. Accordingly, in the illustrated embodiment, both the starting point458 and ending point 460 are selected based on a proportion of diastoleof the cardiac cycle 462. As a result, diagnostic windows defined usingsuch techniques for multiple cardiac cycles may vary from cardiac cycleto cardiac cycle because the length of diastole may vary from cardiaccycle to cardiac cycle. As shown in FIG. 30, a diagnostic window 466 hasbeen identified that includes a starting point 468 and an ending point470 for a cardiac cycle 472 that follows cardiac cycle 462. As a result,the diagnostic window 466 will be longer or shorter than the diagnosticwindow 456, in some instances, because of differences in the length ofdiastole between cardiac cycle 462 and cardiac cycle 472.

While examples of specific techniques for selecting a suitablediagnostic window have been described above, it is understood that theseare exemplary and that other techniques may be utilized. In that regard,it is understood that the diagnostic window is determined using one ormore techniques selected from: identifying a feature of a waveform orother data feature and selecting a starting point relative to theidentified feature (e.g., before, after, or simultaneous with thefeature); identifying a feature of a waveform or other data feature andselecting an ending point relative to the identified feature (e.g.,before, after, or simultaneous with the feature); identifying a featureof a waveform or other data feature and selecting a starting point andan ending point relative to the identified feature; identifying astarting point and identifying an ending point based on the startingpoint; and identifying an ending point and indentifying a starting pointbased on the ending point.

In some instances, the starting point and/or ending point of a maximumdiagnostic window is identified (using one or more of the techniquesdescribed above, for example) and then a portion of that maximumdiagnostic window is selected for use in evaluating the pressuredifferential across a stenosis. For example, in some embodiments theportion selected for use is a percentage of the maximum diagnosticwindow. In some particular embodiments, the portion is between about 5%and about 99% of the maximum diagnostic window. Further, in someinstances, the portion selected for use is a centered portion of themaximum diagnostic window. For example, if the maximum diagnostic windowwas found to extend from 500 ms to 900 ms of a cardiac cycle and acentered portion comprising 50% of the maximum diagnostic window was tobe utilized as the selected portion, then the selected portion wouldcorrespond with the time from 600 ms to 800 ms of the cardiac cycle. Inother instances, the portion selected for use is an off-centered portionof the maximum diagnostic window. For example, if the maximum diagnosticwindow was found to extend from 500 ms to 900 ms of a cardiac cycle andan off-centered portion comprising 25% of the maximum diagnostic windowequally spaced from a mid-point of the maximum window and an endingpoint of the maximum window was to be utilized as the selected portion,then the selected portion would correspond with the time from 700 ms to800 ms of the cardiac cycle. In some instances the diagnostic window isselected for each cardiac cycle such that the location and/or size ofthe diagnostic window may vary from cycle to cycle. In that regard, dueto variances in the parameter(s) utilized to select the beginning, end,and/or duration of the diagnostic window from cardiac cycle to cardiaccycle, there is a corresponding variance in the diagnostic window insome instances.

Referring now to FIGS. 31 and 32, shown therein are aspects ofcalculating a pressure ratio across a stenosis according to anembodiment of the present disclosure. In that regard, FIG. 31 shows adiagnostic window relative to proximal and distal pressure measurements,while FIG. 32 illustrates a temporal adjustment of the distal pressuremeasurement relative to the proximal pressure measurement.

Referring more specifically to FIG. 31, shown therein is a graphicalrepresentation 500 of a proximal pressure 502 and a distal pressure 504over a cardiac cycle of a patient. In that regard, a diagnostic window506 has been identified that includes a starting point 508 and an endingpoint 510. The diagnostic window 506 is suitable for evaluating theseverity of a stenosis of the vessel without the need to use a hyperemicagent. In that regard, the diagnostic window 506, starting point 508,and/or ending point 510 are calculated using one or more the techniquesdescribed above in some instances. As shown, the proximal pressure 502includes a portion 512 coinciding with the diagnostic window 506. Thedistal pressure 504 includes a portion 514 that coincides with thediagnostic window 506.

Referring now to FIG. 32, for a variety of reasons, the proximalpressure 502 and distal pressure 504 are not temporally aligned in someinstances. For example, during data acquisition, there will often be adelay between the distal pressure measurement signals and the proximalpressure measurement signals due to hardware signal handling differencesbetween the instrument(s) utilized to obtain the measurements. In thatregard, the differences can come from physical sources (such as cablelength and/or varying electronics) and/or can be due to signalprocessing differences (such as filtering techniques). In someembodiments, the proximal pressure measurement signal is acquired by androuted through a hemodynamic monitoring system and may takesignificantly longer to reach the processing hardware or computingdevice compared to the distal pressure measurement signal that is sentmore directly to the processing hardware or computing device. Theresulting delay is between about 5 ms and about 150 ms in someinstances. Because individual cardiac cycles may last between about 500ms and about 1000 ms and the diagnostic window may be a small percentageof the total length of the cardiac cycle, longer delays between theproximal and distal pressure measurement signals can have a significantimpact on alignment of the pressure data for calculating a pressuredifferential for a desired diastolic window of a cardiac cycle.

As a result, in some instances, it is necessary to shift one of theproximal and distal pressures relative to the other of the distal andproximal pressures in order to temporally align the pressuremeasurements. In the illustrated embodiment of FIG. 32, a portion of thedistal pressure 504 has been shifted to be temporally aligned with theportion 512 of the proximal pressure 502 coinciding with the diagnosticwindow 506. In that regard, a portion 516 of the distal pressure 504that has been shifted, as indicated by arrow 518, to be aligned with theportion 512 of the proximal pressure 502. While FIG. 32 illustrates ashift of only a portion of the distal pressure 504 into alignment withthe proximal pressure, in other embodiments all or substantially all ofthe proximal and distal pressures are aligned before the portionscorresponding to a selected diagnostic window are identified.

Alignment of all or portion(s) of the proximal and distal pressures isaccomplished using a hardware approach in some instances. For example,one or more hardware components are positioned within the communicationpath of the proximal pressure measurement, the distal pressuremeasurement, and/or both to provide any necessary delays to temporallyalign the received pressure signals. In other instances, alignment ofall or portion(s) of the proximal and distal pressures is accomplishedusing a software approach. For example, a cross-correlation function ormatching technique is utilized to align the cardiac cycles in someembodiments. In other embodiments, the alignment is based on aparticular identifiable feature of the cardiac cycle, such as an ECGR-wave or a pressure peak. Additionally, in some embodiments alignmentis performed by a software user where adjustments are made to the delaytime of at least one of the proximal and distal pressures until thecardiac cycles are visually aligned to the user. A further technique foraligning the signals is to apply a synchronized timestamp at the pointof signal acquisition. Further, in some instances combinations of one ormore of hardware, software, user, and/or time-stamping approaches areutilized to align the signals.

Regardless of the manner of implementation, several approaches areavailable for the aligning the proximal and distal pressure measurementsignals. In some instances, each individual distal pressure measurementcardiac cycle is individually shifted to match the correspondingproximal pressure measurement cardiac cycle. In other instances, anaverage shift for a particular procedure is calculated at the beginningof the procedure and all subsequent cardiac cycles during the procedureare shifted by that amount. This technique requires little processingpower for implementation after the initial shift is determined, but canstill provide a relatively accurate alignment of the signals over thecourse of a procedure because the majority of the signal delay is due tofixed sources that do not change from patient to patient or within theprocedure. In yet other instances, a new average shift is calculatedeach time that the proximal and distal pressure signals are normalizedto one another during a procedure. In that regard, one or more timesduring a procedure the sensing element utilized for monitoring pressuredistal of the stenosis is positioned adjacent the sensing elementutilized for monitoring pressure proximal of the stenosis such that bothsensing elements should have the same pressure reading. If there is adifference between the pressure readings, then the proximal and distalpressure signals are normalized to one another. As a result, thesubsequently obtained proximal and distal pressure measurements are moreconsistent with each other and, therefore, the resulting pressure ratiocalculations are more accurate.

With the proximal and distal pressure measurements aligned, the pressureratio for the diagnostic window 506 is calculated. In some instances,the pressure ratio is calculated using average values for the proximaland distal pressure measurements across the diagnostic window. Thepressure ratio calculations of the present disclosure are performed fora single cardiac cycle, in some instances. In other instances, thepressure ratio calculations are performed for multiple cardiac cycles.In that regard, accuracy of the pressure ratio can be improved byperforming the pressure ratio calculations over multiple cardiac cyclesand averaging the values and/or using an analysis technique to identifyone or more of the calculated values that is believed to be most and/orleast accurate.

Referring now to FIG. 33, shown therein is a graphical representation550 of proximal and distal pressure measurements within a vesselaccording to an embodiment of the present disclosure. In that regard,the graphical representation 550 includes a proximal pressuremeasurement waveform 552 and a distal pressure measurement waveform 554.Generally, the proximal pressure measurement waveform 552 isrepresentative of pressure measurements obtained proximal of a lesion orregion of interest of a vessel and the distal pressure measurementwaveform 554 is representative of pressure measurements obtained distalof the lesion or region of interest of the vessel. The proximal pressuremeasurement waveform 552 has a peak pressure at point 556 and the distalpressure measurement waveform 554 has a peak pressure at point 558. Inthat regard, the peak pressures occur during systole of each heartbeatcycle at or around the systolic wave-free period. In the illustratedembodiment, there is a difference 560 between the peak proximal pressure556 and the peak distal pressure 558. In some embodiments, thedifference 560 is calculated as the peak proximal pressure 556 minus thepeak distal pressure 558. In other embodiments, the difference iscalculated as the peak distal pressure 558 minus the peak proximalpressure 556.

In some instances, this difference between the peak pressures is takeninto account when calculating the ratio of the distal pressure to theproximal pressure during a selected diagnostic window using one or moreof the techniques discussed above. In that regard, the difference 560between the peak proximal pressure 556 and the peak distal pressure 558is determined and then compensated for in making the pressure ratiocalculation. For example, in some embodiments, the difference 560between the peak pressures is added to the distal pressure measurementduring the diagnostic window such that the pressure ratio during thediagnostic window is calculated as (P_(Distal)+Peak PressureDifference)/P_(Proximal). In one such embodiment, the difference iscalculated as the peak proximal pressure 556 minus the peak distalpressure 558. In other embodiments, the difference 560 between the peakpressures is subtracted from the distal pressure measurement during thediagnostic window such that the pressure ratio during the diagnosticwindow is calculated as (P_(Distal)−Peak PressureDifference)/P_(Proximal). In one such embodiment, the difference iscalculated as the peak distal pressure 558 minus the peak proximalpressure 556.

In other instances, a ratio of the peak proximal and distal pressures iscalculated. The ratio of peak pressures can then be used as a scalingfactor to adjust the pressure ratio calculations made during thediagnostic window. For example, in one embodiment, the peak pressureratio is calculated by dividing the peak proximal pressure by the peakdistal pressure. Then the standard pressure ratio calculated across adiagnostic window using one or more of the techniques described abovecan be scaled by multiplying the standard pressure ratio calculation bythe ratio of peak pressures. In this manner, the ratio of peak pressurescan be used as a scaling factor for calculating the pressure ratioduring the diagnostic window. Using either the peak pressure differenceor the peak pressure ratio, differences in pressure present duringsystole can be compensated for when calculating the pressure ratioduring the diagnostic window used to evaluate the vessel. Thiscompensation can be particularly useful in situations where thediagnostic window is selected to be during a wave-free period indiastole following shortly after systole.

Referring now to FIGS. 34 and 35, shown therein are aspects of atechnique for evaluating a vessel according to another embodiment of thepresent disclosure. In that regard, the technique described below withrespect to FIGS. 34 and 35 may be implemented using any of thediagnostic windows and associated techniques discussed above forevaluating a vessel using a pressure ratio across a lesion, stenosis, orregion of interest. However, as will be discussed in greater detail, thetechnique associated with FIGS. 34 and 35 is not dependent upon theaccuracy of the pressure measurements to evaluate the stenosis.Accordingly, concerns about pressure transducer drift during a procedureare largely reduced or eliminated by this technique. Further, the needto repeatedly calibrate or normalize the distal pressure measurementdevice to the proximal pressure measurement device during a procedure islikewise reduced or eliminated.

Referring initially to FIG. 34, shown therein is a graphicalrepresentation 600 illustrating aspects of the technique for evaluatinga vessel according to the current embodiment of the present disclosure.As shown, the graphical representation 600 includes a graph 602 and agraph 604. Graph 602 illustrates a proximal pressure waveform 606 and adistal pressure waveform 608 of a patient over time. Graph 604, in turn,illustrates corresponding calculations based on those waveforms 606 and608. In that regard, plot 610 is representative of a pressure ratio ofthe distal pressure waveform 608 relative to the proximal pressurewaveform 606 over time, which in some embodiments is during a wave freeperiod of the heartbeat cycle. Plot 610 is representative of thepressure ratio calculation used in some of the vessel evaluationtechniques described above. Plot 612 is representative of a slopecomparison between the distal pressure waveform 608 and the proximalpressure waveform 606. In that regard, the slope of the distal pressurewaveform 608 is compared to the slope of the proximal pressure waveform606 to provide an indication of the severity of a lesion or stenosis. Insome instances, a best fit regression slope is utilized. In that regard,one or more of polynomial fitting, multiple line regression, estimationof the slope from points at either end of the waveforms, and/or othersuitable fitting techniques are utilized. Further, the fitting may beperformed over a single heartbeat or over multiple heartbeat cycles.When the slope of the distal pressure waveform 608 is equal to the slopeof the proximal pressure waveform 606, then the polyfit regression slope(i.e., a slope obtained through polynomial curve fitting) will be equalto 1.0, which is indicative of no lesion or stenosis. On the other hand,as the slope of the distal pressure waveform 608 diverges from the slopeof the proximal pressure waveform 606, then the polyfit regression slopemove towards 0.0, which is indicative of a severe lesion or stenosis(e.g., total occlusion or severe blockage). Accordingly, the severity ofthe lesion or stenosis can be evaluated based on the polyfit regressionslope. More specifically, the closer the polyfit regression slope is to1.0 the less severe the lesion/stenosis and the closer the polyfitregression slope is to 0.0 the more severe the lesion/stenosis. Similarto the 0.80 cutoff for pressure ratios discussed above, a predeterminedthreshold value can be utilized for the regression slope comparison. Forexample, in some instances, the predetermined threshold value is betweenabout 0.70 and about 0.90, with some particular embodiments using athreshold value of 0.75, 0.80, 0.85, or otherwise. In other instances,the predetermined threshold value is less than 0.70 or greater than0.90.

As noted above, this slope-based technique is not dependent upon theaccuracy of the pressure measurements to evaluate the stenosis. In thatregard, FIG. 35 illustrates this point. Shown therein is a graphicalrepresentation 620 that includes a graph 622 and a graph 624. Graph 622illustrates a proximal pressure waveform 626 and a distal pressurewaveform 628 of a patient over time. In that regard, proximal pressurewaveform 626 is the same as proximal pressure waveform 606 of FIG. 34and distal pressure waveform 628 is substantially the same as distalpressure waveform 608 of FIG. 34, but to illustrate the effects oftransducer drift the distal pressure waveform 628 has been increased bya constant value of 10 mmHg compared to distal pressure waveform 608.Graph 624 illustrates corresponding calculations based on thosewaveforms 626 and 628. In that regard, plot 630 is representative of apressure ratio of the distal pressure waveform 628 relative to theproximal pressure waveform 626 over time. Notably, the values of plot630 are substantially increased relative to the values of plot 610 ofFIG. 34. This illustrates one of the potential problems of an inaccurateand/or non-normalized distal pressure measurement in the context of thepressure ratio calculation. On the other hand, plot 632 isrepresentative of a slope comparison between the distal pressurewaveform 628 and the proximal pressure waveform 626. As shown, plot 632substantially matches plot 612 of FIG. 34. This is because plots 612 and632 are based upon the shape of the proximal and distal waveforms, whichare the same between FIGS. 34 and 35. In that regard, the distalpressure waveform 628 has the same shape as distal pressure waveform608, it has simply been shifted upward by a value of 10 mmHg. As aresult, plots 612 and 632 based on the slopes of the waveforms arepressure-value independent and, therefore, drift independent. It isunderstood that this waveform shape and/or waveform slope basedtechnique can be implemented using the waveforms from any of thediagnostic windows discussed above.

One advantage of the techniques of the present disclosure foridentifying diagnostic windows and evaluating pressure differentials isthe concept of “beat matching”. In that regard, the proximal and distalwaveforms for the same cardiac cycle are analyzed together with noaveraging or individual calculations that span more than a singlecardiac cycle. As a result, interruptions in the cardiac cycle (such asectopic heartbeats) equally affect the proximal and distal recordings.As a result, these interruptions that can be detrimental to current FFRtechniques have minor effect on the techniques of the presentdisclosure. Further, in some embodiments of the present disclosure, theeffect of interruptions in the cardiac cycle and/or other irregularitiesin the data is further minimized and/or mitigated by monitoring thepressure differential calculations to detect these anomalies andautomatically exclude the impacted cardiac cycles.

In one particular embodiment, pressure ratio is calculated on twosequential cardiac cycles and the individual pressure ratio values areaveraged. The pressure ratio of a third cycle is then calculated. Theaverage value of the pressure ratios is compared to the average pressureratio using three cycles. If the difference between the averages isbelow a predetermined threshold value, then the calculated value isconsidered to be stable and no further calculations are performed. Forexample, if a threshold value of 0.001 is used and adding an additionalcardiac cycle changes the average pressure ratio value by less than0.001, then the calculation is complete. However, if the differencebetween the averages is above the predetermined threshold value, thenthe pressure ratio for a fourth cycle is calculated and a comparison tothe threshold value is performed. This process is repeated iterativelyuntil the difference between the averages of cardiac cycle N and cardiaccycle N+1 is below the predetermined threshold value. As the pressureratio value is typically expressed to two decimal places of precision(such as 0.80), the threshold value for completing the analysis istypically selected to be small enough that adding a subsequent cardiaccycle will not change the pressure differential value. For example, insome instances the threshold value is selected to be between about0.0001 and about 0.05.

In some instances, the level of confidence calculation has differentthresholds depending on the degree of stenosis and/or an initialcalculated pressure ratio. In that regard, pressure ratio analysis of astenosis is typically based around a cutoff value(s) for makingdecisions as to what type of therapy, if any, to administer.Accordingly, in some instances, it is desirable to be more accuratearound these cutoff points. In other words, where the calculatedpressure ratio values are close to a cut-off, a higher degree ofconfidence is required. For example, if the cutoff for a treatmentdecision is at 0.80 and the initial calculated pressure ratiomeasurement is between about 0.75 and about 0.85, then a higher degreeof confidence is needed than if the initial calculated pressure ratiomeasurement is 0.40, which is far from the 0.80 cutoff point.Accordingly, in some instances the threshold value is at least partiallydetermined by the initial calculated pressure ratio measurement. In someinstances, the level of confidence or stability of the calculatedpressure ratio is visually indicated to user via a software interface.For example, the color of the calculated pressure ratio may change asthe confidence level increases (e.g., fading from a darker color to abrighter color), the user interface may include a confidence scale witha corresponding marker displayed for the particular calculation (e.g., asliding scale or a bullseye where an indicator of confidence movescloser to the bullseye as confidence increases), the pressure ratiovalue may transition from a fuzzy or unclear display to a sharp, cleardisplay as confidence increase, and/or other suitable indicators forvisually representing the amount of confidence or perceived precisenessof a measurement.

Because pressure ratio can be calculated based on a single cardiac cyclein accordance with the present disclosure, a real-time or live pressureratio calculation can made while the distal pressure measuring device ismoved through the vessel. Accordingly, in some instances the systemincludes at least two modes: a single-cardiac-cycle mode thatfacilitates pressure ratio calculations while moving the distal pressuremeasuring device through the vessel and a multi-cardiac-cycle mode thatprovides a more precise pressure ratio calculation at a discretelocation. In one embodiment of such a system, the software userinterface is configured to provide the live pressure ratio value untilthe distal pressure measuring device is moved to the desired locationand a measurement button is selected and/or some other actuation step istaken to trigger the multi-cardiac-cycle mode calculation.

Persons skilled in the art will also recognize that the apparatus,systems, and methods described above can be modified in various ways.Accordingly, persons of ordinary skill in the art will appreciate thatthe embodiments encompassed by the present disclosure are not limited tothe particular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

What is claimed is:
 1. A system for evaluating a stenosis of a vessel ofa patient, the system comprising: a physiological guide wire sized andshaped for introduction into the vessel of the patient; a processingunit in communication with the physiological guide wire and apressure-sensing catheter, the processing unit configured to: receiveproximal pressure measurements obtained by the pressure-sensing catheterduring a cardiac cycle of the patient, wherein the proximal pressuremeasurements are obtained without application of a hyperemic agent tothe patient; receive distal pressure measurements obtained by thephysiological guide wire during the cardiac cycle of the patient,wherein the distal pressure measurements are obtained withoutapplication of a hyperemic agent to the patient; select a diagnosticwindow within the cardiac cycle of the patient, wherein a starting pointof the diagnostic window is determined based on at least one of thereceived proximal pressure measurements or the received distal pressuremeasurements and an ending point of the diagnostic window is determinedbased on at least one of the received proximal pressure measurements orthe received distal pressure measurements such that the diagnosticwindow encompasses only a portion of the cardiac cycle of the patient;calculate a pressure ratio based on a plurality of distal pressuremeasurements obtained during the diagnostic window and a plurality ofproximal pressure measurements obtained during the diagnostic window;and output the calculated pressure ratio to a display in communicationwith the processing unit.
 2. The system of claim 1, wherein the startingpoint of the diagnostic window is selected based on a peak pressuremeasurement of at least one of the received proximal pressuremeasurements or the received distal pressure measurements.
 3. The systemof claim 2, wherein the starting point of the diagnostic window isoffset from the peak pressure measurement.
 4. The system of claim 3,wherein the starting point of the diagnostic window is selected based onthe received distal pressure measurements.
 5. The system of claim 2,wherein the ending point of the diagnostic window is selected based onan end of the cardiac cycle.
 6. The system of claim 5, wherein theending point of the diagnostic window is offset from the end of thecardiac cycle.
 7. The system of claim 1, wherein the pressure ratio iscalculated as an average of the plurality of distal pressuremeasurements obtained during the diagnostic window divided by an averageof the plurality of proximal pressure measurements obtained during thediagnostic window.
 8. The system of claim 1, wherein the physiologicalguide wire includes a pressure sensor adjacent a distal end of thephysiological guide wire.
 9. The system of claim 8, wherein thephysiological guide wire further includes a flow sensor adjacent adistal end of the physiological guide wire.
 10. A system for evaluatinga stenosis of a vessel, the system comprising: a processing unit incommunication with at least one intravascular physiological instrument,the processing unit configured to: receive proximal pressuremeasurements and distal pressure measurements for a plurality of cardiaccycles of the patient, wherein the proximal and distal pressuremeasurements are obtained by the at least one intravascularphysiological instrument without application of a hyperemic agent to thepatient; calculate, for a diagnostic window of each of the plurality ofcardiac cycles of the patient, a pressure ratio of the received distalpressure measurements obtained during the diagnostic window and thereceived proximal pressure measurements obtained during the diagnosticwindow, wherein a starting point of the diagnostic window is determinedbased on at least one of the received proximal pressure measurements orthe received distal pressure measurements and an ending point of thediagnostic window is determined based on at least one of the receivedproximal pressure measurements or the received distal pressuremeasurements such that the diagnostic window encompasses only a portionof the cardiac cycle of the patient; calculate an average of thecalculated pressure ratios for the plurality of cardiac cycles of thepatient; and output the calculated average pressure ratio to a displayin communication with the processing unit.
 11. The system of claim 1,wherein the processing unit is further configured to calculate adifference between the calculated average pressure ratio for cardiaccycles 1 to n and the calculated average pressure ratio for cardiaccycles 1 to n+1.
 12. The system of claim 11, wherein the processing unitconfigured to output the calculated average pressure ratio to thedisplay when the difference is below a threshold value.
 13. The systemof claim 12, wherein the threshold value is between about 0.0001 andabout 0.05.
 14. The system of claim 10, further comprising the at leastone intravascular physiological instrument.
 15. The system of claim 14,wherein the at least one intravascular physiological instrumentincludes: a pressure-sensing guide wire configured to obtain the distalpressure measurements; and a pressure-sensing catheter configured toobtain the proximal pressure measurements.
 16. The system of claim 10,wherein the starting point of the diagnostic window is selected based ona peak pressure measurement of at least one of the received proximalpressure measurements or the received distal pressure measurements. 17.The system of claim 16, wherein the starting point of the diagnosticwindow is offset from the peak pressure measurement.
 18. The system ofclaim 17, wherein the starting point of the diagnostic window isselected based on the received distal pressure measurements.
 19. Thesystem of claim 16, wherein the ending point of the diagnostic window isselected based on an end of the cardiac cycle.
 20. The system of claim19, wherein the ending point of the diagnostic window is offset from theend of the cardiac cycle.